Adjustable concave guides for rotary head magnetic tape machines

ABSTRACT

A concave guide is so constructed that the shape of different portions of the guide can be adjusted to selectively change the shape and curvature of the guide. The arrangement is such that the guide can be adjustably deformed to an S-shaped curvature if desired. In the preferred embodiment the guide includes two arms projecting from a point of rigid connection with a body, adjusting screws at the ends of the arms can be manipulated to change the curvature of the arms, and a vacuum source communicates with the guide at the location of connection with the body.

United States Patent Inventor James J. McGlnnls Sunbury, Pa.

Appl. No. 772,651

Filed Nov- 1, 196B Patented July 13, 1971 Anlgnu Forgllo CorporationSunbury, Pl.

ADJUSTABLE CONCAVE GUIDES FOR ROTARY HEAD MAGNETIC TAPE MACHINES T,100.2 C; l78/6.6 A;226/196, 199

Primary Examiner-J. Russell Goudeau Attorney-Markva, Smith & KrugerABSTRACT: A concave guide is so constructed that the shape of differentportions of the guide can be adjusted to selectively change the shapeand curvature of the guide. The arrangement is such that the guide canbe adjustably deformed to an S-shaped curvature if desired. in thepreferred embodiment the guide includes two arms projecting from a pointof rigid connection with a body, adjusting screws at the ends of thearms can be manipulated to change the curvature of the arms, and avacuum source communicates with the guide at the location of connectionwith the body.

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INVENTOR JAMES J MCG/N/ws 54 B2571 .fizvurn ATTORNEY ADJUSTABLE CONCAVEGUIDES FOR ROTARY HEAD MAGNETIC TAPE MACHINES This invention relates toconcave guides for rotary head magnetic tape recording and reproducingmachines, and more particularly to television recording and reproducingapparatus.

In such machines, the tape is usually drawn longitudinally parallel tothe axis of a rotating head drum or wheel on the periphery of which aremounted a series of magnetic heads, spaced angularly from each other,that successively sweep over the tape transversely. A cylindricalconcave vacuum guide is used to maintain the tape in proper relation tothe rotating head wheel or drum.

One of the problems encountered in the operation of such apparatus isdistortion of the data being reproduced. This frequently occurs when atape is recorded on one panel" or machine, and reproduced or played backon another nominally identical panel" or machine, but which may differslightly. Distortion may also occur if the tape has suffered physicaldamage as a result of severe use, even if played back on the same panelon which it was recorded.

There are two distinct types of time base distortion known. One isreferred to as a scallop" distortion, and is due to the fact that thecurvature of the concave guide is not precisely concentric with thecylindrical head wheel or drum because the center of rotation of thedrum is displaced, on the vertical axis, from the center of curvature ofthe guide. Means have been developed in the prior art for adjusting theguide position in such manner as to correct or eliminate this scallop"distortion.

The other type of distortion is known as 8" distortion. It is due to thefact that the panel assembly used to record the tape contained a vacuumguide of slightly different shape than. the vacuum guide contained inthe panel used to play the tape back. It can also be caused by the factthat subsequent to ini tial recording, the tape, and therefore themagnetic data which it contained, suffered physical distortion. In thislatter case, S" will occur even if the playback guide shape is identicalto the shape of the original record guide.

So far as I am aware, no one heretofore hassucceeded in correcting this8" distortion.

The main object of the present invention therefore is to devise meansfor correcting this 8" distortion.

A subsidiary object is to provide means for making the necessaryadjustments while the panel is playing back a test tape, so that theoperator can tell by observation when the distortion has been reduced toa minimum. A second subsidiary object is to provide a means of recording"standard" test tapes having a greater level of tape-to-tape uniformity.

l accomplish this correction of the FS" distortion by forming theconcave vacuum guide with a pair of movable arms arranged to embrace thehead wheel or drum, and by providing means by which these arms may beindividually adjusted so as to cause their inner surface to assume acurvature or shape, which may or may not be a true circular arcconcentric to the center of rotation of the drum, depending upon thesituation causing the distortion, but which will be the optimum or mostnearly correct shape required by the existing geometrical relationshipsbetween the drum, the wheel and the data recorded on the tape.

In order that the invention may be readily understood, reference is hadto the accompanying drawings, forming part. of this specification, andin which:

FIG. 1 is a diagrammatic view illustrating the type of ap' paratus towhich the invention relates;

FIG. 2 is an end elevation ofa panel involving the invention;

FIG. 3 is a horizontal section substantiallyon the line 3-3 of FIG. 2,looking in the direction ofthe arrows;

FIG. 4 is an exploded" perspective view of my improved vacuum guide byitself;

FIG. 5 is a transverse vertical section substantially sn the line 5-5 ofFIG. 3, looking in the direction of the arrows;

FIG. 6 is a diagrammatic view showing the guide relatively too low withrespect to the rotary drum;

FIG. 6A is a diagrammatic view showing the scalloped distortionresulting from the relative position of the parts shown in FIG. 6;

FIG. 7 is a diagrammatic view similar to FIG. 6 but showing the guidetoo high with respect to the rotary drum;

FIG. 7A is a diagrammatic view similar to FIG. 6A but showing thescalloped distortion resulting from the relative position of the partsshown in FIG. 7;

FIG. 8 is a diagrammatic view generally similar to FIGS. 6 and 7 butindicating how the relative position of the parts can be changed tocorrect or eliminate the scalloped distortion;

FIG. 9 is a diagrammatic view similar to FIG. 8 but showing the guide tobe out-of-round, i.e., ellipsoidal with major axis vertical;

FIG. 10 is a diagrammatic view similar to FIGS. 6A and 7A but showingthe species of 8" distortion resulting from the out-of-round conditionshown in FIG. 9;

FIG. II is an enlarged diagrammatic representation of the 8" distortionproduced during a single transverse sweep of a single magnetic headacross the tape during playback when the guide radius is too smalland/or too far away from the wheel in the horizontal direction, and/orwhen the guide is elliptical with major axis vertical, as in FIG. 9;

FIG. 12 is an enlarged diagrammatic representation of the S distortionproduced during a single transverse sweep of a single magnetic headacross the tape during playback when the guide radius is too largeand/or too close to the wheel in the horizontal direction and/or whenthe guide is elliptical with the major axis horizontal;

FIGS. 13A, 13B, 13C and 13D are diagrammatic representations of thegeneral shapes of S distortions produced by various types ofunsymmetrical out-of-round conditions of the vacuum guide duringplayback, as compared with symmetrical conditions during record.

FIGS. 14 and 14A together constitute a single diagram explaining thegeometrical causes for 8" distortion using the case of an out-of-roundguide whose shape approaches that of an ellipse with major axisvertical; and

FIG. 15 is a diagram showing how my improved vacuum guide can beadjusted to eliminate or reduce to an acceptable minimum, the Sdistortion resulting, for example, from an elliptical guide with majoraxis vertical.

Referring to the drawings in detail and first more particularly to FIG.I, the tape 3 is wound on a reel 1 from which it passes around guidepulleys 4 to a takeu p reel 2.

During its travel from one reel to the other it passes through a panel 5on which is mounted a motor 6 driving the head wheel or drum 7 on theperiphery of which are mounted a series of angularly spaced magneticheads 8 which, as the wheel or drum rotates sweep transversely over theconcave surface ofthe tape 3 (see FIG. 2).

Also forming a part of the panel 5 is a vacuum guide 9 having a concaveface 10 (see FIG. 4) which partially embraces the rotary head wheel ordrum one one side, and maintains the tape in the proper shape.

Extending lengthwise of the concave surface of the vacuum guide 9 areone or more grooves 11 (two being shown), and these grooves areconnected by conduits 12 with a passageway 13 formed in the guide 9 andconnected with a source of vacuum by suitable conduit as is perhaps bestshown in FIGS. I and 3.

Referring now to FIGS. 6 to 8, the scalloped distortion is indicated inFIG. 6A at 15 and in FIG. 7A at 16. FIG. 8 indicates diagrammaticallythat the prior art teaches that the guide can be adjusted vertically andhorizontally along the axes X-X and Y-Y so that the guide can be broughtinto true concentric relation with the rotary wheel or drum, and in thisway the scallop distortions 15 and I6 can be corrected or eliminated.

The most serious distortion which, so far as I am aware, no

one has heretofore succeeded in eliminating, is the so-called 8"distortion indicated diagrammatically at I7 in'FIG. I0, and differentforms on an enlarged scale in FIGS. 11, I2, 13A, 13B, 13C and 13D.

FIG. 14A is an enlarged view of one of the distorted lines shown at 17in FIG. 10, and it will be noted that this particular form of "S"distortion consists in the fact that the impulses making up the picture,instead of lying in a straight line 31 as they should, come too early,as indicated at 32, at the upper part of the line and too late asindicated at 34 at the lower part of the line, thus producing areversely curved line of impulses which gives rise to observabledistortion of the picture. Other forms of distortion of either the upperpart 32 of the line or the lower part 34, or both, are also shown inFIGS. 12 and 13A to 13D.

FIG. 14 represents a vacuum guide having an out-of-round condition suchthat its concave surface 28 is more accurately described as a verticalellipse than as a true circular arc. The vacuum guide illustrated isconsidered, for the present purpose, to be in the process of playingback a tape upon which has been recorded a straight vertical line, asshown at 31. The tape was previously record using a truly circularvacuum guide concentrically arranged to the center of rotation of thewheel as suggested by the dashed circular are 29 shown in FIG. 14. Inthe figure, the path of the magnetic head 8 is represented by means of acounterclockwise vector 30. The points 31a through 31a on the circularare 29 indicate the position of the magnetic data on the tape relativeto the path of the head 30 at initial recording. The points 32a through321 on the elliptical concave surface 28 indicate the positions of themagnetic data on the tape relative to the path 30 of the head 8 atplayback." The difference between the relative positions of magneticdata and head path at initial record and the relative positions ofmagnetic data and head path at playback arises because, at record, thetape is positioned with respect to the head path by a circular andconcentric guide while at playback the same tape is positioned by meansof an elliptically shaped guide. To

further explain how distortion occurs, consider the magnetic head 8 atFIG. 14 to be playing back the tape while it is being held in positionby the circular and concentric vacuum guide represented by the circularare 29. It will be noted that the head 8 first comes into radialalignment with data point 31a on 29 and then into radial alignment with31b and so on through 311'. It will be further noted that, in this case,radial alignment of head and magnetic data point occur at the sameangular position of the head as when the data point was initiallyrecorded and, since the head rotates with constant angular velocity, itmay be said that radial alignment occurs at the same time" duringplayback as during record. In other words, during playback the headarrives at each data point exactly on time" with reference to record.Refer now to FIG. 14A. Let the vertical axis 31 contain the distributionof signal impulses produced by the magnetic data points on the tape andlet the horizontal axis 34' represent the time at which the data isplayed back relative to the time" at which it was recorded. In the caseof playback using the same vacuum guide 29 as was used for record, theimpulses are seen to occur on time" and therefore fall upon the verticalor on time axis 31.

With reference again to FIG. 14: consider the magnetic head 8 to beplaying back the same tape as in the foregoing case. In this case,however, the tape is being held in position by the ellipticallyout-of-round vacuum guide surface 28. It will be noted that the head 8first comes into radial alignment with magnetic data point 32a on 28 andthen into radial alignment with 32b and so on through 321'. It will befurther noted that the radial alignment of head and magnetic data pointdoes not occur at the same angular position of the head as when the datapoint was initially recorded. Rather, the head 8 aligns with data point32a on 28 at some time ealier than it aligned with 31a which is the samedate point as 32a except that it is in a different position. As the headcontinues to rotate, it next aligns itself with 32b; again, this occurssome time "earlier" than alignment with 31b. However, alignment with3212 is not quite as early as was head alignment with 3211. Head tomagnetic data point alignment grows less early as the head approachesalignment with 32e at which point the head is ontime." The head nextaligns itself radially with magnetic data point 32f at some small timelater than it aligned with 31]" which is the position of the same datapoint when the tape was being held by the truly circular guide 29. Thehead grows more and more late" as it continues to rotate until itreaches data point 32i at which point is is late" by the same amount oftime that it was early in arriving at data point 32a.

Referring to FIG. 14A, it will be noted that the signal impulsesproduced at alignment of the head 8 with data points 320 through 321'give rise to the reversely curved or distorted" line 32.

It may be pointed out that if the tape in foregoing discussion had beeninitially recorded using the elliptically out-of-round vacuum guideshown in FIG. 9 and/or FIG. 14, then "S distortion would have occurredas a result of "playing back using the circular and concentric guide orany other guide which is not shaped precisely the same as the guide usedfor recording.

The variation of the series of impulses, i.e., so-called 5" distortion,is due to the fact that the shape of the concave inner surface of thevacuum guide used for initial recording of the tape is not the same asthe shape of the concave inner surface of the vacuum guide used forplaying back the tape and therefore, adjusting the guide position alongthe axis x-x and y-y as shown in FIG. 8, will not eliminate nor minimizethe 3" distortion.

I have found that this 8" distortion can be eliminated or reduced to anacceptable minimum by adjusting the shape of the concave inner surfaceof the vacuum guide by means of a construction shown in FIGS. 4 and 5.

By reference to these FIGS. it will be seen that I make up the innerconcave surface of the guide by means of a pair of flexible arms 18,arranged end-to-end, and these meeting ends, being rigidly joined to thebody of the guide by means of an integral portion 18a as best shown inFIG. 5. Other than this integral portion the arms are spaced from thebody substantially throughout their length as indicated at 19 so thatthe arms are free to flex and move relative to the body.

At the upper end of the guide is a nut 20 and at the lower end a nut 21,both nuts being secured firmly to the ends of the arms 18 by means ofscrews 22 passing through openings 23 in the nuts 20 and 21 and engagingthreaded openings 24 in the end portions 18b of the arms 18.

Horizontally and transversely of the guide body 9 adjacent to its upperand lower end are openings 26 through which pass a specially constructedbolt member 25 which I will describe as a differential screw." It isclearly shown in FIGS. 4 and 5 and comprises a relatively large threadedportion 25a engaging a threaded portion 26a of the opening 26.

The bolt or screw 25 has a threaded extension 25b of smaller diameter,and this engages a threaded opening 27 in the nuts 20 and 21. Thisportion of smaller diameter passes freely through an unthreaded opening18 in the ends 18b the arms 18.

Both portions of these special bolts are threaded in the same directionbut each portion has a slightly different lead; thus, when the bolt 25is rotated one turn clockwise the nut 20 will advance to the right (seeFIG. 5) for a distance equal to the differential between the leads ofbolt portions 250 and 25!). This motion will cause the upper flexiblearm to move clockwise with respect to a flexure point located in theintegral body portion 18a. This movement of the flexible arm is shownbest in FIG. 15. By virtue of the differential action of the bolt,extremely fine adjustments of the ends of the arms 18 can be made. Thelower nut 21 preferably has tape guiding lugs 21a projecting from theupper surface thereof.

It will thus be seen that by turning the screws 25 the ends of the arms18 may be moved inwardly or outwardly relative to the body of the vacuumguide, thus altering the radius of cur vature of the concave surface 10of the arms, and changing the shape of the concave surface defined bythese arms. In FIG. IS, the initial shape of the concave surface of theplayback guide is indicated ill 28, while 29 shows the shape of the corncave surface at initial recording. The shape of the concave surface aspartially adjusted, is shown by abroken line at 28a. By

continuing the'adjustment inthe same direction, the line 28a canbe madeto coincide more or lessexactly with 29. In this way, the shape of theconcave surface of the vacuum guide being used to play back aprerecorded tape can be adjusted to conform exactly to or closelyapproach the shape of the concave surface of the vacuum guide initiallyused to record the tape as is best shown in FIG. 15. Thus, 8" distortionat playback is either eliminated or reduced to an acceptable minimum.

It will also be particularly noted that the adjustment of these arms cantake place while a test tape is being run so that the operator can tellby observation exactly when the optimum correction has been made.

What I claim is:

l. A concave vacuum guide to hold a magnetic tape in relation to acylindrical rotating head drum comprising a body, a pair of curved armsdisposed in end to end relation and together providing a continuousconcave surface conforming in general with the cylindrical surface ofsaid drum, said arms being integrally united at their meeting ends, thejunction of such meeting ends being rigidly. secured to said body, saidarms being otherwise spaced from said body throughout their length, saidarms being flexible, and means for independently adjusting the free endsof said arms relative to said body to alter their radius of curvature asdesired.

2. A concave guide in accordance with claim 1 in which said body isprovided with a passageway communicating with a source of vacuum, andthe continuous concave surface of said two arms being formed with atleast one groove connected with said passageway, said groove lying in aplane at substantial right angles to the axis of the head drum,

3. A concave vacuum guide in accordance with claim 1 in which saidadjusting means comprises a screw threaded in an opening in each end ofsaid body and having an extension connected with the free end of thearm, whereby turning said screw will move the free end of said armtoward or away from said body.

4. A concave vacuum guide in accordance with claim 3 in which a nut issecured to the free end of each arm, and said extension is threaded andpasses freely through an opening in the arm but threadedly engages saidnut.

5. A concave vacuum guide in accordance with claim 4 in which theextension of the screw which engages said nut is of smaller diameterthan the main portion of the screw which engages said body, but threadedin the same direction, thus providing a differential screw capable ofmaking extremely fine adjustments.

6. A panel for recording and reproducing television pictures by means ofmagnetic tape, said panel comprising a cylindrical rotary head drumcarrying on its periphery a series of magnetic heads, a concave vacuumguide for said tape having a continuous concave surface embracing saiddrum at one side, and means for selectively changing the curvature ofdifferent portions of the continuous concave surface of said guide.

7. A panel for recording and reproducing television pictures by means ofmagnetic tape, said panel comprising a cylindrical rotary head drumcarrying on its periphery a series of magnetic meads, a concave vacuumguide for said tape having a continuous concave surface embracing saiddrum at one side, and means for changing the shape of the continuousconcave surface of said guide.

8. A concave vacuum guide to hold a magnetic tape in relation to acylindrical rotating head drum comprising a body, curved arm providing acontinuous concave surface conforming in general with the cylindricalsurface of said drum, said arm being rigidly secured to said body at alocation spaced from a free end of the arm, said arm being otherwisespaced from said body throughout its length, said arm being flexible,and means for adjusting at least the free end of said arm relative tosaid body to alter the radius of curvature of the arm.

1. A concave vacuum guide to hold a magnetic tape in relation to acylindrical rotating head drum comprising a body, a pair of curved armsdisposed in end to end relation and together providing a continuousconcave surface conforming in general with the cylindrical surface ofsaid drum, said arms being integrally united at their meeting ends, thejunction of such meeting ends being rigidly secured to said body, saidarms being otherwise spaced from said body throughout their length, saidarms being flexible, and means for independently adjusting the free endsof said arms relative to said body to alter thEir radius of curvature asdesired.
 2. A concave guide in accordance with claim 1 in which saidbody is provided with a passageway communicating with a source ofvacuum, and the continuous concave surface of said two arms being formedwith at least one groove connected with said passageway, said groovelying in a plane at substantial right angles to the axis of the headdrum,
 3. A concave vacuum guide in accordance with claim 1 in which saidadjusting means comprises a screw threaded in an opening in each end ofsaid body and having an extension connected with the free end of thearm, whereby turning said screw will move the free end of said armtoward or away from said body.
 4. A concave vacuum guide in accordancewith claim 3 in which a nut is secured to the free end of each arm, andsaid extension is threaded and passes freely through an opening in thearm but threadedly engages said nut.
 5. A concave vacuum guide inaccordance with claim 4 in which the extension of the screw whichengages said nut is of smaller diameter than the main portion of thescrew which engages said body, but threaded in the same direction, thusproviding a differential screw capable of making extremely fineadjustments.
 6. A panel for recording and reproducing televisionpictures by means of magnetic tape, said panel comprising a cylindricalrotary head drum carrying on its periphery a series of magnetic heads, aconcave vacuum guide for said tape having a continuous concave surfaceembracing said drum at one side, and means for selectively changing thecurvature of different portions of the continuous concave surface ofsaid guide.
 7. A panel for recording and reproducing television picturesby means of magnetic tape, said panel comprising a cylindrical rotaryhead drum carrying on its periphery a series of magnetic meads, aconcave vacuum guide for said tape having a continuous concave surfaceembracing said drum at one side, and means for changing the shape of thecontinuous concave surface of said guide.
 8. A concave vacuum guide tohold a magnetic tape in relation to a cylindrical rotating head drumcomprising a body, curved arm providing a continuous concave surfaceconforming in general with the cylindrical surface of said drum, saidarm being rigidly secured to said body at a location spaced from a freeend of the arm, said arm being otherwise spaced from said bodythroughout its length, said arm being flexible, and means for adjustingat least the free end of said arm relative to said body to alter theradius of curvature of the arm.